[Samsung Galaxy SL i9003] vadexlux:
Ok, not sure when I had to try this command. So I run it while the phone was in normal mode:

C:\Users>adb shell
# /sbin/fat.format /dev/block/mmcblk1p1
/sbin/fat.format /dev/block/mmcblk1p1
fat_init_volume[149]: Check here: No such file or directory

Fail to format
#

Then I entered recovery mode and run in adb while in it:

C:\Users>adb devices
List of devices attached
79600002FFFC0000 recovery

C:\Users>adb shell
# /sbin/fat.format /dev/block/mmcblk1p1
/sbin/fat.format /dev/block/mmcblk1p1
fat_init_volume[149]: Check here: No such file or directory

Fail to format

Here is the recovery log after running the command:

Starting recovery on Fri Oct 7 07:58:13 2011
framebuffer: fd 4 (480 x 800)
ClockworkMod Recovery - for I9003 by Skin1980
recovery filesystem table
=========================
0 /tmp ramdisk (null) (null)
1 /cache rfs /dev/block/stl11 (null)
2 /data rfs /dev/block/mmcblk0p3 (null)
3 /system rfs /dev/block/stl9 (null)
4 /datadata rfs /dev/block/stl10 (null)
5 /sdcard vfat /dev/block/mmcblk1p1 (null)
6 /sd-ext vfat /dev/block/mmcblk0p1 (null)

I:Completed outputting fstab.
I:Processing arguments.
I:Checking arguments.
I:device_recovery_start()
Command: "/sbin/recovery"

ro.secure=0
ro.allow.mock.location=1
ro.debuggable=1
persist.service.adb.enable=1
ro.factorytest=0
ro.serialno=
ro.bootmode=reboot_recovery
ro.baseband=unknown
ro.carrier=unknown
ro.bootloader=unknown
ro.hardware=latona
ro.revision=0
status.battery.state=Slow
status.battery.level=5
status.battery.level_raw=50
status.battery.level_scale=9
ro.build.id=GINGERBREAD
ro.build.display.id=GINGERBREAD.XXKPH
ro.build.version.incremental=XXKPH
ro.build.version.sdk=10
ro.build.version.codename=REL
ro.build.version.release=2.3.4
ro.build.date=Tue Aug 9 21:10:27 KST 2011
ro.build.date.utc=1312891827
ro.build.type=user
ro.build.user=se.infra
ro.build.host=SEP-55
ro.build.tags=release-keys
ro.product.model=GT-I9003
ro.product.brand=samsung
ro.product.name=GT-I9003
ro.product.device=GT-I9003
ro.product.board=GT-I9003
ro.product.cpu.abi=armeabi-v7a
ro.product.cpu.abi2=armeabi
ro.product.manufacturer=samsung
ro.product.locale.language=en
ro.product.locale.region=GB
ro.wifi.channels=
ro.board.platform=omap3
ro.build.product=GT-I9003
ro.build.description=GT-I9003-user 2.3.4 GINGERBREAD XXKPH release-keys
ro.build.fingerprint=samsung/GT-I9003/GT-I9003:2.3.4/GINGERBREAD/XXKPH:user/release-keys
ro.build.PDA=I9003XXKPH
ro.build.hidden_ver=I9003XXKPH
ro.build.changelist=467143
ro.flash.resolution=720
rild.libpath=/system/lib/libsec-ril.so
rild.libargs=-d /dev/ttyS0
wifi.interface=eth0
ro.sf.lcd_density=240
dalvik.vm.heapsize=64m
ro.opengles.version=131072
persist.service.usb.setting=0
ro.config.ringtone=01_Minimal_tone.ogg
ro.config.notification_sound=01_Sherbet.ogg
ro.config.alarm_alert=Good_Morning.ogg
ro.url.legal=http://www.google.com/intl/%s/mobile/android/basic/phone-legal.html
ro.url.legal.android_privacy=http://www.google.com/intl/%s/mobile/android/basic/privacy.html
ro.com.google.locationfeatures=1
ro.setupwizard.mode=DISABLED
ro.com.google.clientidbase=android-samsung
ro.com.google.gmsversion=2.3_r5
wifi.supplicant_scan_interval=15
ro.secdevenc=true
ro.wtldatapassword=true
keyguard.no_require_sim=true
ro.com.android.dateformat=MM-dd-yyyy
ro.com.android.dataroaming=true
ro.ril.hsxpa=1
ro.ril.gprsclass=10
media.stagefright.enable-player=false
media.stagefright.enable-meta=false
media.stagefright.enable-scan=false
media.stagefright.enable-http=true
media.stagefright.enable-rtsp=false
dalvik.vm.dexopt-flags=m=y
net.bt.name=Android
net.change=net.bt.name
dalvik.vm.stack-trace-file=/data/anr/traces.txt
ro.bt.bdaddr_path=/efs/bluetooth/bt_addr
init.svc.console=running
init.svc.recovery=running
init.svc.adbd=running

I:Checking for extendedcommand...
I:Skipping execution of extendedcommand, file not found...
mount: mounting /dev/block/mmcblk1p1 on /sdcard failed: No such file or directory
W:failed to mount /dev/block/mmcblk1p1 (File exists)
W:failed to mount /dev/block/mmcblk1p1 (No such file or directory)
E:Can't mount /sdcard